Plant to pollinate

Janet Wade explores how corn is pollinated and what effect this has on the end result.

The pollination process of corn may seem to be merely interesting trivia, but it has a big influence on how we should plant and manage our crop to get the best results.

A corn plant has separate male and female flowers. The male flowers grow along the branched stalk that sprouts from the top of the plant. The cluster of flowers is called the tassel. The female flowers are found in the ear, halfway down the plant, and turn into the juicy kernels of corn that we eat – but not until they are pollinated.

The male flowers release a lightweight pollen that is blown about by the wind. When a pollen grain lodges on one of the sticky strands of silk growing from the ear (one from each immature kernel of corn) it grows a pollen tube down the inside of the silk and fertilises the kernel. Those silks may be a nuisance when we come to cook the corn, but they are highly necessary!

For the best chance of pollination, corn should be planted in blocks of at least four rows of four plants with the plants spaced around 30cm apart and the rows 1m apart. If the plants are in a single row, spread around the garden; one here, one there; or only a couple of plants are put in, the result is likely to be a crop of dry cobs or cobs with missing kernels. You often see this at the top of corn cobs because the silks start growing from the bottom and the tassels run out of pollen before the top silks develop. However, if there is only space for a few plants, they can be hand-pollinated. One way is to tap the tassels over a paper bag then brush the collected pollen over the silks with a paintbrush. The process should be repeated each day until the flowers stop producing pollen.

1: The male flowers produce pollen that is carried on the wind.2: Wind-borne pollen is caught by the silks of the female flower. One strand is attached to each kernel of corn.3: To maximise the chance of pollination corn should always be planted in a block. 4: Most corn plants produce two cobs, but it is usually only the top one that fully develops. This is mostly because of the tassels running out of pollen.5: Corn cobs are ready to harvest when the silks start to brown, the ears point away from the stalks at a roughly 45-degree angle, and the juice of the kernels runs white when pierced by a thumbnail.

The kernels of some corn varieties, such as ‘Supersweet’, won’t be true to type if the plants cross-pollinate with other varieties, and any sweetcorn cross-pollinated with popcorn or ornamental corn will have tough starchy kernels. If you want to grow more than one variety, the easiest way around this in the home garden is to plant the different varieties at least 10 days apart, since the tassels usually produce their pollen over a 10-day period.

It is best to wait until the weather warms up at the beginning of summer to start your corn, because the seeds will rot rather than germinate if the soil is cold and wet, and the days need to be dry when it comes time for the tassels to release their pollen. Corn is best grown from seeds sown direct into the garden, but will tolerate careful transplant from seed trays. Sow two seeds together (removing the weaker seedling once they sprout) in a position in full sun, in a bed enriched with plenty of compost, animal manure and a nitrogen-rich general fertiliser. Do this well before planting time so that the nitrogen doesn’t harm the emerging roots. The seedlings will need to be protected from the attentions of birds and slugs and snails.

Corn’s fast growth uses up a lot of nutrients, so the plants can benefit from a side-dressing when the tassels start to develop, with the same nitrogen-rich general fertiliser used before planting. The plants need to be kept watered so there is no check in growth. This becomes particularly important once the tassels appear and the kernels begin filling out. The ears are usually ready to harvest around two to three weeks after pollination, when the silks start to brown and the ears point away from the stems. If in doubt, peel the husk back slightly and pierce one of the kernels with your thumbnail. When the corn is ripe the juice will be milky rather than clear. And that is when it all becomes worth it. Because corn cobs quickly convert their sugars to starch and lose their sweetness, the taste of store-bought corn cobs doesn’t compare with those taken straight from the garden to the kitchen.